grafspee

It is called propeller rpm control. By moving it forward or backward you only set target rpm for governor, so when you are on the ground and you are idling engine at 1200rpm, moving this rpm do absolutely nothing, propeller pitch does not change. I don't think so that any war time US manual will call it pitch lever. In order to increase rpm governor will decrease pitch, lower pitch means lower AoA of the prop blades and this mean lower drag and this mean that prop can spin faster with same amount of power. Americans and British call it differently but way that it works is the same. You move this lever forward you get lower/fine pitch if anything else is constant.

By Increasing pitch you reduce rpm. There is no prop pitch lever in p51. There is only rpm control lever if you move it full forward governor will lower pitch to maintain 3000. If rpm drops below 3000 while this level is full on this mean that prop pitch is at low pitch stop. Prop pitch in p51 is in the governor hands, pilot can not set pitch directly. You can move rpm lever full back and prop pitch will remain in full fine pitch stop, you can set rpm at max and prop pitch can be very close to coarse pitch stop. You are saying one thing and doing opposite. I would not start this conversation if you discribe it right.

Then we are playing 2 different games. In my version of dcs if i want to slow down faster i cut throttled and if this not enought increase rpm to max. And if i want to glide as far as possible when my engine gives up i reduce rpm to minimum. @kablamoman showed you video which explains this topic.

Maybe during high alt high speed dives, but for level flight can't be, going supersonic instantly kills thrust generated by this part of the blade and if prop reduction gear got small adjustment top speed would increase significantly.

I doubt that tip of the prop exceeds speed of sound ever. Tip velocity may go close to speed of sound. P-51 manual also states that in case of prop governor failure pilot can operate engine up to 3250rpm even at those rpm tip isn't supersonic.

Do you really think that reducing rpm increase drag so plane slows down faster? It maybe shock you but going high pitch or feather position (which is the highest pitch you can set) reduce drag and make that plane can glide much further. Going in to low pitch (rpm lever full forward) prop generates the highest drag possible thus slowing plane down much faster. Higher windmill rpm = higher power required = higher kinetic energy drain simple as that.

Engine RPM affects peak working pressure and how long it act on piston. Fuel has effective octane rating this is why WW2 fuel are rated 100/130 or 100/145 first number is effective octane rating for lean mixture and second is for rich mixture. Higher peak pressure combine with longer piston action (in terms of time = Lower RPM ) results that engine makes more out of air-fuel mixture charge. Higher RPM = more cycles per time = more power / Higher RPM lowers peak working pressure so engine can be operated safely at higher manifold pressure Lower RPM = higher working pressure and expansion time = higher efficiency / Lower RPM increase working pressure so engine can not be operated safely at high manifold pressure / High MP at low rpm will result in working pressure exceeding effective octane rating parameters of the fuel resulting in detonations and quick engine death. RPM is only related to engine, optimal Prop RPM is set by engine to prop reduction gear, if engine could operate at 5000 rpm prop rpm would be the same because optimal prop rpm depends on prop diameter.

@Gunfreak This is why i countless times bring this issue on this forum since i joined it. I just can't imagine situation when after let say 15 minute of intense combat pilot had to drop power leave battle and his friends. Famous WEP issue in DCS P-51 starting since i joined here with hard coded script which kills engine once you use WEP, i remember ppl were recording this famous loud bang after they landed and shut off engine. I don't know if this issue is fixed or not but DCS successfully discouraged me from ever breaking WEP wire in P-51, i just don't do that so i don't get irritated by engine seizing I can bring another over sensitivity The famous P-47's main engine bearing, which in first introduction was insane sensitive. Till now it isn't fixed completely because engine gives up way before 3060rpm red line which according to manuals this 3060 rpm red line is cleared for up to 30s. In DCS you pass 2850 or so and engine is toasted. In arcade games those hard limits are introduced to prevent players from firewalling engines because in gaming you don't care if your engine will last 400 hours, 1 to 2 hours is the max and every time you take fresh plane, ofc there are players who are trying to go back to base refuel and take off again as many times as they can but this arcadish modeling prevent them from succeeding in this endeavor. I'm not sure if those engines in DCS can survive 10 hours of life time. In hardcore simulator like DCS i won't accept those arcade engine limiters.

Running engine at 3000rpm won't damage it, it will increase engine weare and shorten engine life time but it will not damage it. And P-51 manual states that engine goes for full tear down inspection after 5 hours of accumulated WEP usage so NO, engines weren't replaced after single use of WEP. You could probably could go for more then hour of continuous wep before engine would give up. That would shorten engine life time to couple hours but life time of p51 engine was aimed for couple hundreds hours so equivalent time limitations were used

If you want use full boost +18lbs you have to use 3000rpm, at 2850rpm you are limited to about +12lbs at 2650rpm you are limited to +7lbs. So in combat patrol i would use 2850 rpm and boost up to 12 and going in to combat i would increase rpm to 3000rpm and work throttle then, you don't have to fire wall throttle 100% of time in combat but make sure that you use max rpm so engine can take full boost.

@virgo47 On top of that, all this values like power, crit alt , fuel flow are for v-1650-3 engine and engine simulated in DCS P-51 is V-1650-7. V-1650-7 61/3000rpm S.L outputs 1590hp and war emergency is 1700hp but at lower alt. High blower alt with ram air for military power is around 26k ft. -3 can hold 61 inch well above 30k which is totally impossible for -7

It could be many things, overcooling, not proper warming up , over stressing power settings for engine could be a bug too as well hard to say without track.

Provide track with failure. This is the best way to find out what is happening.

Pretty much all thermostatic valves in coolant circuits consist small opening which is opened even when valve is completely closed, reason for this is to push a little bit of hot coolant to other side of valve so it can react quicker and with better precision, so in theory if you would cut throttle completely and put plane into long dive temp could drop below 60C but it would took a lot of time. Flying at even very low power like boost +0 at 2000rpm this setup should hold that 80C with no problem. Another positive factor of this thermostatic valve is that warming engine up especially in sub zero temp will happen very fast due to that coolant flow through radiator is near zero up to 80C. P-51 had special attachment, for cold weather to prevent overcooling in flight, which restrict flow through belly air scoop.

In spitfire coolant circuit should consist thermostatic valve which should prevent coolant temp going down too much. Iirc temp set was 80C. In p51 temp is regulated via actuating shutter doors in spitfire those shutter doors have 2 fixed positions with no intermediate positions.

This is very accurate, in 44 Germans were outnumbered 10 fold.

Even if there is no MW50 in tank you can still use 1.8 ATA but you can do this only at very high alt. And don't bother using manual cooling set it for auto and that's it.

@Gunfreak There were many during WW2 which had problems with aim. So you are not alone.

@Roosterfeet 38inch at 2400 rpm by all means should not kill engine, by heaving rpm and MP in green zone automatic mixture control will lean mixture for cruise. The more important thing is how you reduce or increase power. If you want to reduce power always retard throttle first for desired MP and then reduce rpm to proper level. In case when you increase power first set rpm then MP.

@MAD-MM I am aware of bug report about oil temp in P-51 that oil temp can go off grid and engine feels fine. But i don't know if fix came in. I know that in DCS features come in and are taken away constantly. Maybe cooling is still worked on or just team switched to something else and with newer patches things fades away. @Nealius Those are my temps in climb. To force system to work with lower temps is as fallows. If you intend to climb with 180mph enter this climb and steep it so you lose speed to 150mph keep it there for a while and then drop nose and get to 180mph this trick forces system to open shutters but once you drop nose and accelerate temps will drop but not enough to trigger shutter closing temps and there you go with that simple trick you can control coolant/oil temp in some extent w/o playing with coolant switches. Ofc you can manually open shutter and flip them back to auto this should work as well but i haven't test it.

Last time i checked it will blow relieve valve and vent coolant until almost all coolant is gone. Everyone know that if water boils it stops gaining temp and adding heat only intensifies boiling process, same here in P-51 temp at which relieve valve opens will remain steady while coolant is boiling and only when major of it goes out temp will climb further up. Unless relieve valve won't be able to even excess pressure in time and pressure in system will go up then coolant temp will go up as well.

I've hit 97c at high alt max power dogfight.

Our P-51 is late war model, where oil and other stuff was improved. Setting higher temps improves performance of the plane, you need much wider opening to keep 100C then to keep 113C coolant temp. In later P-51 manuals you can find that 95C oil temp was allowed while using WEP. But engine optimal temps won't change. You still get green temps while cruising at medicore power range. But for climb or combat power temps will get higher. Green arc on gauges represents optimal temp range but operating temp range is much larger iirc for coolant it is 60C to 121C and for oil 15C to 90C ofc with respect to oil pressure limits.

Redline for coolant is 121C and for oil 90C. I fly P-51 quite often and in auto mode temps are always below redline, and this is only what matters, automatic shutters aren't set up to maintain temps in green zone as P-51 maintenance manual states. Oil cooler doors won't open until 87C of oil temp is reached. Same with coolant, shutter door won't move until temp goes way above green zone. In case of the coolant temp gauge it may be 2 times thickness of the needle. In climb you will always be above green zone and this is totally fine.

Can you specify what "very hot coolant and oil temps" mean, 46" 2700rpm is max continuous. Automatic cooling shutters system has hysteresis, opening and closing temps for shutters are spread. I can't remember exactly but opening coolant shutter temp is something like 110C and closing is something like 100C same with oil cooler shutter 87C opening and 80 closing temp, can't remember exact numbers it could be that coolant opening is at 113C. When your coolant/oil temp is 112C/86C automatic system will not open coolers shutter doors, but if you increase power and those temps ticks up by 1C automatic system will start opening shutters and it will stop opening them when temps will drop below opening temps, at this point you have slight opened cooler shutters and if you reduce power and coolant and oil temp will drop by 5C automatic system will not adjust cooler shutters, it will react only when coolant/oil temp drop below closing temps. That way when you are flying at 46" and 2700rpm temps can be as low as closing temps and as high as opening temps at same speed same OAT same power setting.